Hypertensive response to thiopental in man during cardiopulmonary bypass

We report the effect of 250 mg of sodium thiopental on vascular tone at constant blood flow in 26 patients undergoing cardiopulmonary bypass while the ascending aorta was cross-clamped. Light anaesthesia was effected with fentanyl and enflurane, muscle relaxation with pancuronium. After a latent period of 10.5 +/- 0.7 s there was a hypertensive response of 9.8 +/- 0.5 s duration and of 21.4 +/- 1.7 mmHg (2.8 +/- 0.2 kPa) magnitude; this was followed by hypotension of 39.6 +/- 4.2 s duration and of 18.4 +/- 1.9 mmHg (2.4 +/- 0.3 kPa) magnitude. There was a statistically significant inverse correlation between the hypertension and body temperature (P = 0.005); the time to onset of hypertension correlated directly with pump volume (P = 0.001), weight of the patient (P = 0.03), and cross-clamp time before the drug was given (P = 0.002), and correlated inversely with the serum sodium concentration (P = 0.001). The duration of hypertension was inversely related to the plasma bicarbonate (P = 0.01) and body temperature (P = 0.04). The duration of hypotension was significantly longer in women (P = 0.0001) and was directly related to the duration of cross-clamping (P = 0.0007), to pH (P = 0.0016), and to PCO2 (P = 0.04). We speculate that thiopental induced the hypertensive response due to a potentiation of the vasoconstrictive (local) effect of norepinephrine, and induced the hypotensive response by a central nervous system effect. Thiopental had no apparent effect on venous tone.